Internal mold release agent for use in reaction injection molding

ABSTRACT

The preent invention is directed to an internal mold release composition comprising: 
     (a) a zinc carboxylate selected from the group consisting of zinc stearate, zinc laurate and zinc oleate, and 
     (b) a compatibilizer comprising a dispersion of polyurea and/or a polyhydrazodicarbonamide in an organic compound containing at least one hydroxyl group, in an amount sufficient to solubilize the zinc carboxylate. 
     The invention also relates to the use of such composition.

BACKGROUND OF THE INVENTION

Reaction injection molding (RIM) has become an important process for the production of external automotive body parts and other types of molded products. The RIM process involves the intimate mixing of a polyisocyanate component and an isocyanate-reactive component followed by the injection of this mixture into a mold for subsequent rapid curing. The polyisocyanate component is typically based on a liquid polyisocyanate. The isocyanate-reactive component contains a high molecular weight isocyanate-reactive component, typically a polyol and/or amine polyether, and usually contains a chain extender containing amino and/or hydroxyl groups. U.S. Pat. No. 4,218,543 describes a RIM process currently being commercially used on a large scale.

While products produced by the RIM process have excellent physical properties, the use of the RIM process was previously limited by the necessity of using sprayed external mold release agents (e.g., waxes, soaps, and the like). These agents had to be sprayed onto the mold surface before each shot or every several shots. Recently, internal mold release agents have become available which obviate the need for external release agents. Specifically internal mold release agents containing zinc carboxylates where the carboxylate group contains from 8 to 24 carbon atoms has met with widespread commercial use. Release agents of this type are described in U.S. Pat. Nos. 4,519,965, 4,581,386 and 4,585,803; and British Patent No. 2,101,140. In using such zinc carboxylates it is necessary to mix the carboxylate with a compatibilizer which will solubilize the zinc carboxylate so that when the resultant mixture is mixed with the isocyanate-reactive components, the zinc carboxylate will possess improved resistance to precipitation. British Patent No. 2,101,140 describes the mixture of a zinc stearate and an epoxidized vegetable oil (such as epoxidized soybean oil).

U.S. Pat. Nos. 4,519,965 and 4,581,386 describe the use of compatibilizer selected from the group consisting of nitrogen-containing, isocyanate-reactive acyclic compounds and nitrogen-containing, isocyanate-reactive polymers. Preferred compatibilizers include polyether polyamines and amine- or hydroxy-terminated, amine-initiated polyethers. U.S. Pat. No. 4,585,803 describes the use of compatibilizers which are tertiary amine compounds which contain at least one tertiary nitrogen. The tertiary amine compounds described advantageously contain one or more hydroxy groups.

Although the combination of the zinc carboxylates and the compatibilizers noted have met with substantial commercial success, the search continues for other satisfactory compatibilizers.

DESCRIPTION OF THE INVENTION

The present invention is directed to a novel internal mold release agent for use in a RIM process, to an isocyanate-reactive component containing the mold release agent, and to the use of the mold release agent in a RIM process.

The internal mold release agent of the present invention comprises:

(a) a zinc carboxylate selected from the group consisting of zinc stearate, zinc laurate and zinc oleate, and

(b) a compatibilizer comprising a dispersion of a polyurea and/or a polyhydrazodicarbonamide in an organic compound containing at least one hydroxyl group, in an amount sufficient to solubilize the zinc carboxylate.

Suitable zinc carboxylates which may be used in the internal release agent mixture of the present invention are zinc stearate, zinc oleate and zinc laurate.

The preferred zinc carboxylates are those which remain soluble in combination with the compatibilizer when in admixture with the high molecular weight isocyanate-reactive component and the chain extender. The most preferred zinc carboxylate is zinc stearate, especially those having a high purity such as Zinc Stearate Polymer Grade Type N from Witco, Zinc Stearate RSN 131 HS and IPS from Mallinckrodt and Zinc Stearate Heat Stable Polymer Grade from Nuodex. In the RIM systems the zinc carboxylates are used in amounts of about 0.5 to 10%, preferably about 1 to 6% and most preferably about 1 to 4% by weight, based on the weight of the isocyanate-reactive components.

Suitable compatibilizers are those of the type noted which assist in compatibilizing or solubilizing the zinc carboxylates without substantially affecting the processing characteristics of the RIM reaction mixture or the physical property or paintability of the resultant molded articles. More particularly, the compatibilizers of the present invention comprise a dispersion of a polyurea and/or a polyhydrazodicarbonamide in an organic compound containing at least one hydroxyl group. These dispersions are known in the art, are commercially available, and have been described, e.g., in U.S. Pat. Nos. 3,525,421, 4,042,537; 4,089,835, 4,293,470, 4,296,213 and 4,374,209, the disclosures of which are herein incorporated by reference. In general, the dispersions useful herein are produced by reacting monofunctional, difunctional or higher functional isocyanates with (a) polyamines containing primary and/or secondary amino groups and/or (b) hydrazines and/or hydrazides, in the presence of an organic compound which contains at least one hydroxyl group. As is known and as described in the above-noted U.S. patents, such dispersions can be produced having a wide range of solids contents. In general, the solids content of the dispersion itself will range from 1 to as high as 40 percent, and preferably from 5 to 40 percent by weight.

The mold release compositions of the present invention are suitable for the use with either flexible or rigid, optionally cellular, polyurethane or polyurea elastomers. The molded articles may possess various combinations of these properties such as rigid, non-cellular elastomers or flexible, cellular products for use, e.g., as shoe soles. "Polyurethanes" as defined throughout this application are polyaddition products wherein urethane groups and optionally urea groups are formed during the RIM process according to the invention. "Polyureas" are defined as polyaddition products wherein only urea groups are formed during the RIM process according to the invention.

The present invention is also directed to an isocyanate-reactive mixture comprising

(i) a high molecular weight polymer having at least two isocyanate-reactive groups and having a molecular weight of from 400 to about 10,000,

(ii) from about 5 to 50% by weight, based on the weight of component (i) of a chain-extender having at least two isocyanate-reactive groups and

(iii) an internal mold release agent mixture comprising:

(a) from about 0.05 to about 10% by weight, based on the weight of components (i) and (ii) of a zinc carboxylate selected from the group consisting of zinc stearate, zinc laurate and zinc oleate, and

(b) a compatibilizer comprising a dispersion of a polyurea and/or a polyhydrazodicarbonamide in an organic compound containing at least one hydroxyl group, in an amount sufficient to solubilize the zinc carboxylate so that when component (iii) is in admixture with components (i) and (ii), the zinc carboxylate possesses improved resistance to precipitation.

Finally the present invention is directed to a process for the production of optionally cellular parts by reacting a reaction mixture comprising the isocyanate-reactive component which contains the internal mold release with a polyisocyanate, said reaction mixtures being processed by the RIM process at an isocyanate index of from 70 to 130.

Suitable polyisocyanates for use in the present invention are aliphatic, cycloaliphatic, araliphatic, aromatic and heterocyclic polyisocyanates which are known and described for example by W. Siefken in Justus Liebigs Annalen der Chemie, 562, pages 75-136. Specific examples include ethylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,12-dodecane diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1,3- and -1,4-diisocyanate and mixtures thereof, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane (isophorone diisocyanate or IPDI), 2,4- and 2,6-hexahydrotoluylene diisocyanate and mixtures thereof, hexahydro-1,3- and/or -1,4-phenylene diisocyanate, perhydro-2,4'- and/or -4,4'-diphenyl methane diisocyanate, 1,3- and 1,4-phenylene diisocyanate, 2,4- and 2,6-toluene diisocyanate and mixtures thereof, diphenyl methane 2,4'- and/or 4,4'-diisocyanate, naphthylene 1,5-diisocyanate, triphenyl methane-4,4',4"-triisocyanate and polyphenyl polymethylene polyisocyanates of the type obtained by condensing aniline with formaldehyde, followed by condensation.

It is preferred to use the readily available polyisocyanates such as 2,4- and 2,6-toluene diisocyanate and mixtures of these isomers, polyphenyl polymethylene polyisocyanates of the type obtained by condensing aniline with formaldehyde, followed by phosgenation, and polyisocyanates containing carbodiimide groups, urethane groups, allophanate groups, isocyanurate groups, urea groups or biuret groups. Particularly preferred are the liquid derivatives of 4,4'-diphenyl methane diisocyanate (MDI) which may be liquefied inter alia by introducing carbodiimide groups, blending with 2,4'-diphenyl methane diisocyanate or by introducing urethane groups. Especially preferred are the liquefied derivatives of MDI prepared by reacting MDI with 0.1 to 0.3 mols of a polypropylene glycol having a molecular weight of up to about 700, in particular, dipropylene glycol, tripropylene glycol or mixtures thereof as disclosed for example in U.S. Pat. No. 3,644,457.

Also suitable for use as the polyisocyanate component are isocyanate-terminated prepolymers based on the above-mentioned polyisocyanates and the isocyanate-reactive compounds, preferably hydroxyl compounds, disclosed hereinafter for use in accordance with the present invention. Prepolymers of this type are disclosed in U.S. Pat. No. 4,374,210. The prepolymers are preferably based on the polyether or polyester polyols disclosed hereinafter and, optionally, the low molecular weight, hydroxyl group-containing chain extenders which are also disclosed hereinafter. Blends of any of the previously disclosed polyisocyanates may also be used in accordance with the present invention.

Other suitable reactants for preparing the molded products of the present invention include compounds containing at least two isocyanate-reactive groups. These compounds may be divided into two groups, high molecular weight compounds having a molecular weight of 400 to about 10,000 and low molecular weight compounds, i.e. chain extenders, having a molecular weight of 62 to 399. Examples of suitable high molecular weight compounds include the polyesters, polyethers, polythioethers, polyacetals and polycarbonates containing at least 2, preferably 2 to 8 and most preferably 2 to 4 isocyanate-reactive groups of the type known for the production of polyurethanes.

The high molecular weight polyethers suitable for use in accordance with the invention are known and may be obtained, for example, by polymerizing epoxides such as ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, styrene oxide or epichlorohydrin in the presence of BF₃ or by chemically adding these epoxides, preferably ethylene oxide and propylene oxide, in admixture or successively to components containing reactive hydrogen atoms such as water, alcohols or amines. Examples of alcohols and amines include the low molecular weight chain extenders set forth hereinafter, 4,4'-dihydroxy diphenyl propane, sucrose, aniline, ammonia, ethanolamine and ethylene diamine. It is preferred to use polyethers which contain substantial amounts of primary hydroxyl groups in terminal positions (up to 90% by weight, based on all of the terminal hydroxyl groups present in the polyether). Polyethers modified by vinyl polymers of the type formed for example, by polymerizing styrene or acrylonitrile in the presence of polyether (U.S. Pat. Nos. 3,383,351; 3,304,273; 3,523,093; and 3,110,695; and German Patent No. 1,152,536), are also suitable, as are polybutadienes containing OH groups.

In addition, polyether polyols which contain high molecular weight polyadducts or polycondensates in finely dispersed form or in solution may be used. Such modified polyether polyols are obtained when polyaddition reactions (e.g., reactions between polyisocyanates and amino functional compounds) or polycondensation reactions (e.g., between formaldehyde and phenols and/or amines) are directly carried out in situ in the polyether polyols.

Suitable examples of high molecular weight polyesters include the reaction products of polyhydric, preferably dihydric alcohols (optionally in the presence of trihydric alcohols), with polyvalent, preferably divalent, carboxylic acids. Instead of using the free carboxylic acids, it is also possible to use the corresponding polycarboxylic acid anhydrides or corresponding polycarboxylic acid esters of lower alcohols or mixtures thereof for producing the polyesters. The polycarboxylic acids may be aliphatic, cycloaliphatic, aromatic, and/or heterocyclic and may be unsaturated or substituted, for example, by halogen atoms. The polycarboxylic acids and polyols used to prepare the polyesters are known and described for example in U.S. Pat. Nos. 4,098,731 and 3,726,952, herein incorporated by reference in their entirety. Suitable polythioethers, polyacetals, polycarbonates and other polyhydroxyl compounds are also disclosed in the above identified U.S. patents. Finally, representatives of the many and varied compounds which may be used in accordance with the invention may be found for example in High Polymers, Volume XVI, "Polyurethanes, Chemistry and Technology," by Saunders-Frisch, Interscience Publishers, New York, London, Vol. I, 1962, pages 32-42 and 44-54, and Volume II, 1964, pages 5-6 and 198-199; and in Kunststoff-Handbuch, Vol. VII, Vieweg-Hochtlen, Carl Hanser Verlag, Munich, 1966, pages 45-71.

Suitable aminopolyethers which may be used in accordance with the present invention as high molecular weight compounds (the molecular weight is always the average molecular weight which may be calculated from the functionality and the content of isocyanate-reactive groups) are those wherein at least about 30 and preferably about 60 to 100 equivalent % of the isocyanate-reactive groups are primary and/or secondary (preferably primary) aromatically or aliphatically (preferably aromatically) bound amino groups and the remainder are primary and/or secondary aliphatically bound hydroxyl groups.

In these compounds, the terminal residues carrying the amino groups may also be attached to the polyether chain by urethane or ester groups. These "aminopolyethers" are prepared by methods known per se. For example, polyhydroxypolyethers such as polypropylene glycol ethers may be aminated by reaction with ammonia in the presence of Raney nickel and hydrogen (BE-PS 634,741). U.S. Pat. No. 3,654,370 describes the production of polyoxyalkylene polyamines by reaction of the corresponding polyol with ammonia and hydrogen in the presence of a nickel, copper, chromium catalyst. DE-PS No. 1,193,671 describes the production of polyethers containing terminal amino groups by hydrogenation of cyanoethylated polyoxypropylene ethers. Other methods for the production of polyoxyalkylene (polyether) amines are described in U.S. Pat. Nos. 3,155,728, 3,236,895 and FR-PS No. 1,551,605. The production of polyethers containing terminal secondary amino groups is described, for example, in FR-PS No. 1,466,708.

Polyhydroxypolyethers of relatively high molecular weight may be converted into the corresponding anthranilic acid esters by reaction with isatoic acid anhydride, as described, for example, in DE-OS Nos. 2,019,432 and 2,619,840 and in U.S. Pat. Nos. 3,808,250, 3,975,428 and 4,016,143. Polyethers containing terminal aromatic amino groups are formed in this way.

According to DE-OS No. 2,546,536 and U.S. Pat. No. 3,865,791, relatively high molecular weight compounds containing terminal amino groups are obtained by reaction of NCO prepolymers based on polyhydroxypolyethers with enamines, aldimines or ketimines containing hydroxyl groups and subsequent hydrolysis.

It is preferred to use amino polyethers obtained by hydrolysis of compounds containing terminal isocyanate groups, for example in accordance with DE-OS No. 2,948,419 or U.S. Pat. No. 4,515,923, herein incorporated by reference in its entirety. In this process, polyethers most preferably containing 2 to 4 hydroxyl groups are reacted with polyisocyanates to form NCO prepolymers and, in a second step, the isocyanate groups are converted by hydrolysis into amino groups.

The "aminopolyethers" used in accordance with the invention are often mixtures of the compounds mentioned by way of example and (on a statistical average) most preferably contain 2 to 4 terminal isocyanate-reactive groups. In the process according to the invention, the "aminopolyethers" may be used in admixture with polyhydroxypolyethers free from amino groups.

In accordance with the present invention, the high molecular weight compounds are used in admixture with up to about 95% by weight, preferably up to about 50% by weight, more preferably about 8 to 30% by weight and most preferably about 12 to 26% by weight, based on the total quantity of the high molecular weight compounds, of the low molecular weight chain extenders. Examples of suitable hydroxyl group-containing chain extenders include ethylene glycol, 1,2- and 1,3-propane diol, 1,3- and 1,4- and 2,3-butane diol, 1,6-hexane diol, 1,10-decane diol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, glycerol and trimethylol propane.

Other suitable chain extenders include aromatic polyamines, preferably diamines, having molecular weights of less than 400, especially the sterically hindered aromatic polyamines, preferably diamines, having molecular weights of less than 400, especially the sterically hindered aromatic diamines which contain at least one linear or branched alkyl substituent in the ortho-position to the first amino group and at least one, preferably two linear or branched alkyl substituents containing from 1 to 4, preferably 1 to 3, carbon atoms in the ortho-position to a second amino group. These aromatic diamines include 1-methyl-3,5- diethyl2,4-diamino benzene, 1-methyl-3,5-diethyl-2,6- diamino benzene, 1,3,5-trimethyl-2,4-diamino benzene, 1,3,5-triethyl-2,4-diamino benzene, 3,5,3',5'-tetra- ethyl-4,4'-diamino diphenylmethane, 3,5,3',5'-tetra-isopropyl-4,4'-diamino diphenylmethane, 3,5-diethyl-3',5'-diisopropyl-4,4'-diamino diphenylmethane, 3,5-diethyl-5,5'-diisopropyl-4,4'-diamino diphenylmethane, 1-methyl-2,6-diamino-3-isopropylbenzene and mixtures of the above diamines. Most preferred are mixtures of 1-methyl-3,5-diethyl-2,4-diamino benzene and 1-methyl-3,5-diethyl-2,6-diamino benzene in a weight ratio between about 50:50 to 85:15, preferably about 65:35 to 80:20.

In addition, aromatic polyamines may be used in admixture with the sterically hindered chain extenders and include, for example, 2,4- and 2,6-diamino toluene, 2,4'- and/or 4,4'-diamino-diphenyl-methane, 1,2- and 1,4-phenylene diamine, naphthalene-1,5-diamine and triphenylmethane-4,4',4"-triamine. The difunctional and polyfunctional aromatic amine compounds may also exclusively or partly contain secondary amino groups such as 4,4'-di-(methylamino)-diphenylmethane or 1-methyl-2-methylamino-4-amino-benzene. Liquid mixtures of polyphenyl polymethylene-polyamines, of the type obtained by condensing aniline with formaldehyde, are also suitable. Generally, the nonsterically hindered aromatic diamines and polyamines are too reactive to provide sufficient processing time in a RIM system. Accordingly, these diamines and polyamines should generally be used in combination with one or more of the previously mentioned sterically hindered diamines or hydroxyl group-containing chain extenders.

Other additives which may be used in the present invention include catalysts, especially tin(II) salts of carboxylic acids, dialkyl tin salts of carboxylic acids, dialkyl tin mercaptides, dialkyl tin dithioesters and tertiary amines. Preferred among these catalysts are dibutyl tin dilaurate and 1,4-diazabicyclo-(2,2,2)-octane (triethylene diamine), especially mixtures of these catalysts. The catalysts are generally used in amounts of about 0.01 to 10%, preferably about 0.05 to 2%, based on the weight of the high molecular weight component.

It is also possible to use surface-active additives such as emulsifiers and foam stabilizers. Examples include N-stearyl-N',N'-bis-hydroxyethyl urea, oleyl polyoxyethylene amide, stearyl diethanol amide, isostearyl diethanolamide, polyoxyethylene glycol monoleate, a pentaerythritol/adipic acid/oleic acid ester, a hydroxy ethyl imidazole derivative of oleic acid, n-stearyl propylene diamine and the sodium salts of castor oil sulfonates or of fatty acids. Alkali metal or ammonium salts of sulfonic acid such as dodecyl benzene sulfonic acid or dinaphthyl methane sulfonic acid and also fatty acids may also be used as surface-active additives.

Suitable foam stabilizers include water-soluble polyether siloxanes. The structure of these compounds is generally such that a copolymer of ethylene oxide and propylene oxide is attached to a polydimethyl siloxane radical. Such foam stabilizers are described in U.S. Pat. No. 2,764,565. In addition to the catalysts and surface-active agents, other additives which may be used in the molding compositions of the present invention include known blowing agents, cell regulators, flame retarding agents, plasticizers, dyes, fillers and reinforcing agents such as glass in the form of fibers or flakes or carbon fibers.

The compositions according to the present invention may be molded using conventional processing techniques and are especially suited for processing by the RIM process. In general, two separate streams are intimately mixed and subsequently injected into a suitable mold, although it is possible to use more than two streams. The first stream contains the polyisocyanate component, while the second stream contains the polyol component, chain extender, the internal mold release agent mixture and any other additive which is to be included.

The invention is further illustrated but is not intended to be limited by the following examples in which all parts and percentages are by weight unless otherwise specified.

In the examples the dispersion used was a commercially available dispersion having an OH number of about 28 and consisting of a polyhydrazodicarbonamide in a glycerin initiated propylene oxide/ethylene oxide polyether with an OH number of 35, and produced by reacting toluene diisocyanate and hydrazine hydrate in the presence of the polyether, according to U.S. Pat. No. 4,089,835. The dispersion has a solids content of 20 percent by weight and a maximum water content of 0.50 percent by weight.

EXAMPLES EXAMPLE 1

A clean dry flask equipped with a mechanical stirrer, heating mantle, thermometer, nitrogen inlet and reflux condenser, was charged with 3000 parts of the above dispersion and heated to 135° C. 150 parts of zinc stearate were slowly added with stirring. Heating was continued for one hour after the addition was complete. The mixture was allowed to cool to room temperature with stirring. A stable dispersion resulted.

EXAMPLE 2

Using the same technique as Example 1, 333 parts of zinc stearate were dispersed in 4667 parts of the dispersion. A stable dispersion resulted.

EXAMPLE 3

Using the same technique as Example 1, 200 parts of zinc stearate were dispersed in 2000 parts of the dispersion. A stable dispersion resulted.

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims. 

What is claimed is:
 1. An internal mold release composition comprising:(a) a zinc carboxylate selected from the group consisting of zinc stearate, zinc laurate and zinc oleate, and (b) a compatibilizer comprising a dispersion of polyurea and/or a polyhydrazodicarbonamide in an organic compound containing at least one hydroxyl group, in an amount sufficient to solubilize the zinc carboxylate.
 2. The composition of claim 1, wherein component (a) is zinc stearate.
 3. The composition of claim 1, wherein component (b) is produced by reacting a monofunctional, difunctional or higher functional isocyanate with (i) a polyamine containing primary and/or secondary amino groups and/or (ii) a hydrazine and/or a hydrazide, in the presence of said organic compound.
 4. An isocyanate-reactive composition comprising(i) a high molecular weight polymer having at least to isocyanate-reactive groups and having a molecular weight of from 400 to about 10,000, (ii) from about 5 to 50% by weight, based on the weight of component (i) of a chain-extender having at least two isocyanate-reactive groups and (iii) an internal mold release agent mixture comprising:(a) from about 0.05 to about 10% by weight, based on the weight of components (i) and (ii) of a zinc carboxylate selected from the group consisting of zinc stearate, zinc laurate and zinc oleate, and (b) a compatibilizer comprising a dispersion of a polyurea and/or a polyhydrazodicarbonamide in an organic compound containing at least one hydroxyl group, in an amount sufficient to solubilize the zinc carboxylate so that when component (iii) is in admixture with components (i) and (ii), the zinc carboxylate possesses improved resistance to precipitation.
 5. The composition of claim 4 wherein component (iii)(a) is zinc stearate.
 6. In a process for producing a molded part by reacting an isocyanate with an isocyanate-reactive component in a mold, the improvement wherein the reaction mixture includes an internal mold release composition comprising(a) a zinc carboxylate selected from the group consisting of zinc stearate, zinc laurate and zinc oleate, and (b) a compatibilizer comprising a dispersion of polyurea and/or a polyhydrazodicarbonamide in an organic compound containing at least one hydroxyl group, in an amount sufficient to solubilize the zinc carboxylate. 